Purpose:
To estimate the scleral and lamina cribrosa (LC) material properties for nonhuman primate (NHP) eyes by comparison of eye-specific finite element (FE) models to serial histologic reconstructions of eye pairs from which acute IOP-related connective tissue deformation was characterized.
Methods:
3D reconstructions of the ONH were generated for 3 pairs of normal NHP eyes perfusion-fixed at IOP of 10mmHg(OS) and 45mmHg(OD). Connective tissue deformation was characterized using a 3D histomorphometric technique and distilled into two parameters: scleral canal expansion (SCE) and LC displacement (LCD) [IOVS 2009, 50(12)]. Finite element (FE) models of posterior pole were generated for the 10mmHg eyes using an established method [IOVS 2009 August 20, Epub]. Model constants for the scleral and LC elastic moduli were fitted such that the SCE and LCD in the pressurized FE models matched that measured histologically in the contralateral high-IOP eye.
Results:
We were able to fit LC and scleral material constants such that the FE model deformations matched both SCE and LCD experimental data well for all three eyes. NHP 3 exhibited a large amount of SCE experimentally, and the models fit to the experimental LCD and SCE data was less precise (8-15% error). Estimated scleral elastic modulus values derived from the model’s fitted parameters (10.4, 7.4, 5.9 MPa) were within the range of previous experimental values for NHP sclera [IOVS 50(11):5226-37]. The LC material constants fell in the range used for previous modeling work.
Conclusions:
These results demonstrate that material properties for specimen-specific FE models can be tuned to capture the histologically-measured deformation behavior of ONH connective tissues, thereby providing estimates for the scleral and laminar material properties for an individual eye. Such a fitting technique could provide a powerful means of clinically estimating patient-specific material properties when used in conjunction with emerging technologies like deep-scan SD-OCT.
Keywords: lamina cribrosa • intraocular pressure • computational modeling